In computer networks, it is often desirable to measure link delay between network equipment located in different geographic locations. In symmetric networks where the link delay is the same or nearly the same in both directions between two locations, the one-way link delay (i.e., the delay in one direction from one device to a remote device) can be measured by transmitting a packet from one location to the other and back, recording the round-trip time, and dividing the round-trip time by two. However, in asymmetric networks, the delay in one direction is different from the delay in the other direction. As a result, dividing the round-trip time by two is an inaccurate measure of one-way link delay in asymmetric networks.
One method for measuring link delay in an asymmetric network is to use specialized equipment that is capable of egress packet time stamping and swapping the roles of receive and transmit ports to determine the link delay in each direction. For example, some optical networking equipment includes transmit and receive ports whose roles can be reversed. To measure link delay in one direction, a packet can be sent from a transmit port of one device to a receive port of another device. The outgoing packet is time stamped by the transmitting device and its time of receipt is recorded by the receiving device using its local time. The roles of the receive and transmit ports are then reversed and the process is repeated in the opposite direction, by also adding the receive time of the first packet. The one-way link delay can be determined based on the difference between the transmit and receive times of the packet of both the forward and the reverse path.
It may be desirable to measure link delay in optical, wireless, or electrical networks where specialized network equipment capable of port role reversal is not available. In addition, some network equipment may not be able to generate timestamps for outgoing packets. In such networks, another mechanism needs to be provided to accurately measure one-way link delay.
Accordingly, there exists a need for methods, systems, and computer readable media for measuring one-way link delay.